Seiko 3423A – Technical Guide

The Seiko 3423A is a compact, manual-winding mechanical movement designed for ladies' wristwatches, part of Seiko's 34xx movement family. Built during the late 1960s and 1970s, this caliber reflects Seiko's commitment to durability, slim design, and precise timekeeping in small, elegant cases. The 3423A is closely related to the 3421A but features minor internal adjustments, mainly in the gear train or bridge layout.

This technical guide outlines the movement’s specifications, construction, maintenance process, and common service issues.

Movement Overview

• Caliber Number: 3423A

• Type: Mechanical (manual winding)

• Functions: Hour and Minute only

• Size: 6¾ × 8 lignes (approx. 15.3 mm × 17.8 mm)

• Thickness: ~3.15 mm

• Jewels: 17

• Beat Rate: 21,600 vibrations per hour (6 beats per second)

• Power Reserve: Approximately 38–42 hours

• Hacking Seconds: No

• Date Function: None

The 3423A is known for its clean layout, reliable performance, and suitability for slim-profile dress watches.

Mechanical Features

Despite its small dimensions, the Seiko 3423A follows traditional mechanical architecture, engineered for longevity:

Core Components:

• Mainspring Barrel: Wound via the crown; provides power to the gear train.

• Center, Third, Fourth, and Escape Wheels: Step down the gear ratio to regulate timekeeping.

• Pallet Fork & Escape Wheel: Transmit precise energy bursts to the balance wheel.

• Balance Assembly: Controls oscillations and ensures time regulation.

• Shock Protection: Seiko’s Diashock system typically installed on the balance.

• Bridges and Plates: Made of rhodium- or nickel-plated brass with a compact bridge layout.

This movement contains no complications (like date or seconds), which helps improve longevity and reduces service complexity.

Servicing the 3423A

Recommended Service Interval:

• Every 3–5 years

Standard Service Steps:

1. Disassemble the movement, including dial and hands, and carefully separate the balance, gear train, and mainspring.

2. Clean components in an ultrasonic cleaner (except balance and hairspring, which should be cleaned manually).

3. Inspect pivots, jewels, and the mainspring for wear or fatigue.

4. Lubricate using modern oils (Moebius or equivalent) at pivots, escapement, and mainspring arbor.

5. Reassemble with precision, ensuring smooth gear alignment.

6. Regulate the balance using a timing machine. Target ±30 seconds/day for vintage accuracy.

⚠️ Note: Spare parts may be hard to source. Donor movements or vintage parts suppliers are often required for restorations.

Common Issues and Solutions

Conclusion

The Seiko 3423A is a charming, compact hand-wound mechanical movement that showcases Seiko’s dedication to precise engineering in small calibers. Its two-hand, no-date design reduces mechanical complexity and makes it ideal for slim, elegant women's timepieces. With regular maintenance and careful handling, the 3423A remains a reliable and collectible movement worthy of restoration and continued use.